1. Field of the Invention
The present invention relates to a multilayer flexible substrate including two types of different regions: a rigid region and a flexible region that is more flexible than the rigid region.
2. Description of the Related Art
Increasingly downsized electronic devices, such as notebook personal computers and cellular phones, are requiring thin, flexible mounting boards to optimize limited mounting spaces. Such a mounting board is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2000-183526. With reference to FIG. 3, a multilayer wiring board 100 disclosed in Japanese Unexamined Patent Application Publication No. 2000-183526 includes a laminate 103 including insulating substrates 101 and wires 102 alternately stacked, through-holes 104 disposed in the insulating substrates 101, and filled vias formed by filling the through-holes 104 with a conductor 105. The wires 102 are electrically connected to each other through the filled vias. The laminate 103 includes a bending portion 106 formed by partially reducing the thickness of the laminate 103.
The multilayer wiring board 100 includes a structure including rigid portions located at both ends of the multilayer wiring board 100 and the bending portion 106, which connects these two portions and is flexible. In this structure, the rigid portions are referred to as “rigid regions” and the bending portion 106, which connects the two rigid portions, is referred to as a “flexible region”. A substrate having such a structure is referred to as a “multilayer flexible substrate”. A multilayer flexible substrate is a type of circuit board.
When manufacturing such a multilayer flexible substrate, wires have been connected to each other through the same filled vias disposed in rigid regions and a flexible region. However, when the filled vias are disposed in the flexible region, there is a problem in that flexibility sufficient to bend the multilayer flexible substrate is not achieved because the filled vias reduce the flexibility of the flexible region.